Heat exchangers are carried on waste heat recovery systems or EGR coolers. The heat exchangers carried on the waste heat recovery systems are designed such that heat of exhaust gas generated by engines warms cooling water, as disclosed in JP 2001-241872 A.
FIG. 15 hereof shows how to assemble a heat exchanger disclosed in JP 2001-241872 A. At first, a fin 101 having top and bottom portions 101a, 101b is inserted into a fin case 102 with brazing material applied onto the top and bottom portions 101a, 101b. Second, the fin case 102 is compressed to bring the fin 101 into contact with an interior surface of the fin case 102. Such a compressed fin case 102 is provided in plural. The compressed fin cases are inserted into end plates 103, 103 in such a manner that opposite ends of the compressed fin cases are held by the end plates 103, 103. The compressed fin cases with the opposite ends held by the enc plates 103, 103 are then housed in a core case 104. This core case 104 undergoes a brazing operation within a brazing furnace to form a heat exchanger 105.
The heat exchanger 105 is designed such that exhaust gas flows inside each of the fin cases 102 and cooling water flows outside each of the fin cases 102 so as to transfer heat of the exhaust gas to the cooling water.
One may propose improving heat transfer efficiency of the heat exchanger 105 by increasing the heat transfer area, for example, by providing each of the fin cases 102 with a pair of upper and lower fins 107a, 107b. The heat exchanger 105 having the upper and lower fins 107a, 107b will be discussed below with reference to FIG. 16.
As shown in FIG. 16, the fins 107a, 107b are housed in the fin case 102. The fin case 102 housing the fins 107a, 107b is provided in plural. The fin cases 102 are inserted into the end plates 106 and housed in the core case 104, in the manner as discussed above. The core case 104 is formed into a heat exchanger 105′ by undergoing brazing operation in the manner as stated above to form a heat exchanger.
The heat exchanger 105′ including the two fins 107a, 107b provides larger heat transfer area than the heat transfer area of the heat exchanger 105 having the single fin 101. As shown in FIG. 16, furthermore, the upper fin 107a has a bottom 108 which does not contact a top 109 of the lower fin 107b. The heat exchanger 105′ with the bottom 108 spaced from the top 109 provides a larger heat transfer area than with the top 109 in contact with the top 109.
In manufacturing the heat exchanger having such fins 107a, 107b, however, the fin case 102 is subjected to a brazing operation with undesirable loads applied to the fin case 102 in a direction towards an inside of the fin case 102, as shown by arrows of FIG. 16. The application of the loads to the fin case 102 would plastically deform the fin case 102.
When the heat exchanger 105′ is used for a waste heat recovery system, furthermore, cooling water flows around the fin case 102 in which case the fin case 102 would be plastically deformed under pressure from the cooling water.
There is a need for a heat exchanger having high strength in addition to providing a larger heat transfer area.